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ABC News has learned that Eric Nordstrom, the former Regional Security Officer at the U.S. Embassy in Libya, has told congressional investigators that security at the U.S. diplomatic post in Benghazi, Libya, was "inappropriately low" - and believed that State Department officials stood in the way of his attempts to change that.

Nordstrom and the commander of a 16-member Security Support Team, Lieutenant Colonel Andrew Wood, heard that foreign fighters were flowing across the Egyptian border and were making their way across the border to the Libyan city of Derna - which is to the east of Benghazi - and from there were making their way to Benghazi. But State Department officials seemed oblivious to their Benghazi post's vulnerability.

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Nordstrom was worried -he did not know how much the Americans could rely on members of a local Libyan militia in Benghazi that provided security - the "17th of February Martyrs Brigade." Mostly merchants and shopkeepers before the war, they seemed eager, but they hadn't much experience and other than a daily $30 stipend for food from the U.S. Embassy, they hadn't been paid in months.

Nordstrom had "no idea if they would respond to an attack," he told investigators.

The House Oversight and Government Reform Committee, led by Rep. Darrell Issa, R-Calif., will hold hearings on what went wrong today at noon ET. Nordstrom will testify at that hearing.

Nordstrom twice wrote to the State Department - in March and July 2012 - to beef up the presence of American security officers in Benghazi, but neither time was there a response. At no point from December 2011 through July 2012, when he left Libya, were more than three Diplomatic Security Service agents permanently and simultaneously stationed at the Benghazi post.

Nordstrom wanted at least five personnel to be stationed at Benghazi, but the State Department would not allow it. There were American security officers, however, at the U.S. Embassy in Tripoli, including three Mobile Security Detachments, which were part of the DSS, and a 16-member Security Support Team detailed from Special Operations Command AFRICOM, commanded by Wood. But the State Department would not give him permission to deploy them to be stationed at Benghazi. Deputy Assistant Secretary for international programs Charlene Lamb, in Nordstrom's view, wanted to keep the number of U.S. security personnel in Benghazi "artificially low," according to a memo for Democrats on the House Oversight Committee.

Wood, a former Green Beret, told ABC News that he and other members of the Security Support Team wanted to remain in Libya past their deployment was scheduled to end in August, and that Ambassador Stevens wanted them to remain as well. Nordstrom has said that Lamb told him not to request for the Security Support Team to be extended again. (Its deployment had been previously extended in February 2012.)

Lamb will testify before the House committee later today.

"I do recall one conversation with her where she (Lamb) said that since we now had a residential safe haven in Benghazi that she didn't seem to have a problem with having no agents on the compound because if something happened then personnel could simply go to that residential safe haven," Nordstrom told investigators.

That safe haven proved a deathtrap. Situated inside the main residence in Benghazi, consisting of three bedrooms and a bathroom set aside from the rest of the building by metal grillwork and several locks, the safe haven is where Stevens and information officer Sean Smith suffered severe smoke inhalation after the attackers set the house on fire.

On Tuesday afternoon, State Department officials acknowledged that despite earlier explanations from the Obama administration, there was no protest outside the Benghazi compound at all. Only an hour before gunmen methodically and deliberately stormed the post, the streets were empty and everything seemed calm. Obama administration officials originally claimed the trouble began with demonstrations against an anti-Muslim video, a protest that, U.S. Ambassador to the United Nations Susan Rice told ABC News' THIS WEEK on the Sunday after the attack, "seems to have been hijacked, let us say, by some individual clusters of extremists."

Rice and White House officials now say those initial accounts were based on early intelligence, since corrected. State Department officials now call the attack unprecedented given the number of gunman, weapons and lethal force used.

-Jake Tapper